Research ArticleAPPLIED SCIENCES AND ENGINEERING

Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphones

See allHide authors and affiliations

Science Advances  03 Aug 2018:
Vol. 4, no. 8, eaas8772
DOI: 10.1126/sciadv.aas8772
  • Fig. 1 Fabrication of freestanding hybrid NMs with orthogonal AgNW arrays.

    (A) Schematic of fabrication procedure for freestanding hybrid NMs with orthogonal AgNW arrays embedded in a polymer matrix. (B) Freestanding AgNW composite NMs floating on a surface of water. Scale bar, 1 cm. (C) Dark-field optical microscope image of orthogonal AgNW arrays. The inset shows an FFT image of the optical micrograph, corresponding to its surface geometric structure. Scale bar, 40 μm. (D) Cross-sectional SEM image of an as-fabricated hybrid NM on a ZnO/Si substrate. Scale bar, 100 nm. (E) Optical transmittance of polymer NMs, hybrid NMs, bare PET, and bare glass in the visible range of 400 to 800 nm. The air is used as a reference. (F) Photograph of a hybrid NM on the surface of water under compressive force applied by a glass rod. Scale bar, 3 mm. (G) A freestanding hybrid NM supported by a wire loop. Inset shows the high transparency of the hybrid NM. Scale bar, 1 cm. (H) Hybrid NMs transferred onto curvilinear surface and (I) onto human skin.

  • Fig. 2 Conformal contact of AgNW composite hybrid NMs on 3D microstructures.

    (A) Schematic of conformal contact of NMs on the skin surface. (B) Hybrid NMs attached to a thumb. The inset shows a micrograph of a hybrid NM on the skin of a fingertip. Scale bar, 1 mm. (C and D) SEM images of the hybrid NMs transferred on line-patterned 3D PDMS microstructures with a line width of 20 μm (C) and 120 μm (D). Scale bars, 50 and 100 μm, respectively. The insets show magnified images with scale bars indicating 10 μm (C) and 50 μm (D). SEM images of hybrid NMs with thicknesses of 40 nm (E), 100 nm (F), and 200 nm (G) transferred onto micropyramid-patterned 3D PDMS microstructures with a diameter of 10 μm and a height of 7 μm. Scale bars, 5 μm.

  • Fig. 3 Mechanical properties of hybrid NMs with orthogonal AgNW arrays.

    (A) Freestanding hybrid NMs with different densities of orthogonal AgNW arrays floating on the water surface. NMs are wrinkled by a water droplet of radius ≈ 0.3 mm. The number of wrinkles decreases as the density of the AgNWs increases. Scale bars, 200 μm. (B) Young’s modulus (E) of NMs as calculated from the wrinkle tests. (C) Comparison of calculated and experimental bending stiffness of hybrid NMs with orthogonal AgNW arrays of different densities. We calculated the measured bending stiffness using the Young’s modulus that had been experimentally obtained with the capillary wrinkling method. (D) Applied indentation load versus displacement of freestanding hybrid NMs as a function of the density of orthogonal AgNW arrays. (E) Maximum indentation load versus displacement of hybrid NMs as a function of orthogonal AgNW arrays.

  • Fig. 4 Skin-attachable NM loudspeaker.

    (A) Schematic of the skin-attachable NM loudspeaker with the orthogonal AgNW array. Sound is generated by temperature oscillation produced by applying an AC voltage. (B) Acoustic measurement system where sound emitted from the NM loudspeaker is collected by a commercial microphone with a dynamic signal analyzer. (C) Variation in sound pressure (SP) generated from the NM loudspeaker and the thick-film loudspeaker as a function of the input power at 10 kHz. (D) Experimental and theoretical values of SPL versus sound frequency for NM and thick PET film loudspeakers. (E) Skin-attachable NM loudspeaker mounted on the back of a hand. Scale bar, 1 cm.

  • Fig. 5 Wearable and transparent NM microphone.

    (A) Schematic of a wearable NM microphone device. (B) Transparent NM microphone placed over the “UNIST” logo, illustrating its transparent and unobtrusive appearance. Scale bar, 1 cm. (C) Sensing measurement system for the NM microphone. Variation in the output voltages as a function of (D) sound frequency and (E) SPL for the NM microphone and the thin-film microphone. (F) Waveform and short-time FFT (STFT) signals of original sound (“There’s plenty of room at the bottom”; left) extracted by the sound wave analyzer, the signal read from the NM-based microphone (middle), and the thin-film microphone (right).

  • Fig. 6 Personal voice-based security system.

    (A) Schematic of the voice security system (left) and a photograph of the authorization process using the freestanding NM microphone (right). (B) Sound waveforms and (C) voiceprints collected from the registrant, the authorized user, and the denied user using the NM microphone. (D) Matching probability of voiceprint for the authorized user using the NM microphone and a commercial microphone. (E) Matching probability of voiceprints obtained from different users including the registrant, a man, and two women. Photo credit: Saewon Kang.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaas8772/DC1

    Section S1. The calculated bending stiffness of the thin film

    Section S2. The measured bending stiffness of the thin film

    Fig. S1. Fabrication of the freestanding hybrid NM with the orthogonal AgNW array by removing the sacrificial layer.

    Fig. S2. Total thickness of the hybrid NM measured by atomic force microscopy.

    Fig. S3. Transmittance in the visible range of 400 to 800 nm and corresponding sheet resistance, Rs, of the orthogonal AgNW array with different numbers of orthogonal coatings.

    Fig. S4. The structural design of the hybrid NM for the calculation of the bending stiffness with geometrical parameters illustrated.

    Fig. S5. SEM images of the hybrid NM folded in half.

    Fig. S6. High-magnitude SEM images of the hybrid NM transferred on the line-patterned PDMS with a line width of 20 μm.

    Fig. S7. Estimated step surface coverage of the hybrid NMs with different thickness placed on a micropyramid-patterned PDMS substrate.

    Fig. S8. Number of wrinkles generated from a pure parylene NM and hybrid NMs.

    Fig. S9. Variation in the number of wrinkles N as a function of N ~ a1/2h−3/4.

    Fig. S10. Indentation test for measuring the mechanical properties of NMs.

    Fig. S11. Loading-unloading indentation test.

    Fig. S12. IR images of the orthogonal AgNW array with AC 10 V applied at a frequency of 10 kHz.

    Fig. S13. SPL versus distance between the commercial microphone and the thick-film loudspeaker with the orthogonal AgNW array.

    Fig. S14. Theoretical values of SPL as a function of sound frequency for loudspeaker with different thickness and substrates.

    Fig. S15. Comparison of adhesion force of various micropatterned PDMS films.

    Fig. S16. Schematics showing the structure of microphone devices.

    Fig. S17. Waveform and STFT signals of original sound (“There’s plenty of room at the bottom”) extracted by the sound wave analyzer, where the signal was read from a commercial microphone.

    Fig. S18. FFTs extracted from the sound wave of the word “nanomembrane” obtained from voices of different subjects including the registrant, the authorized user, and the denied user.

    Fig. S19. FFTs extracted from the sound wave, obtained from the voice of a registrant.

    Fig. S20. FFTs for a test repeated 10 times, extracted from the sound wave of the word “hello” obtained from various voices of different subjects including the registrant, a man, and two women.

    Movie S1. Mechanical durability of hybrid NM.

    Movie S2. Compression and stretching test of hybrid NM.

    Movie S3. Skin-attachable NM loudspeaker.

    Movie S4. The voice recognition using NM microphone.

    Movie S5. Voice-based security system.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. The calculated bending stiffness of the thin film
    • Section S2. The measured bending stiffness of the thin film
    • Fig. S1. Fabrication of the freestanding hybrid NM with the orthogonal AgNW array by removing the sacrificial layer.
    • Fig. S2. Total thickness of the hybrid NM measured by atomic force microscopy.
    • Fig. S3. Transmittance in the visible range of 400 to 800 nm and corresponding sheet resistance, Rs, of the orthogonal AgNW array with different numbers of orthogonal coatings.
    • Fig. S4. The structural design of the hybrid NM for the calculation of the bending stiffness with geometrical parameters illustrated.
    • Fig. S5. SEM images of the hybrid NM folded in half.
    • Fig. S6. High-magnitude SEM images of the hybrid NM transferred on the line-patterned PDMS with a line width of 20 μm.
    • Fig. S7. Estimated step surface coverage of the hybrid NMs with different thickness placed on a micropyramid-patterned PDMS substrate.
    • Fig. S8. Number of wrinkles generated from a pure parylene NM and hybrid NMs.
    • Fig. S9. Variation in the number of wrinkles N as a function of N ~ a1/2h−3/4.
    • Fig. S10. Indentation test for measuring the mechanical properties of NMs.
    • Fig. S11. Loading-unloading indentation test.
    • Fig. S12. IR images of the orthogonal AgNW array with AC 10 V applied at a frequency of 10 kHz.
    • Fig. S13. SPL versus distance between the commercial microphone and the thick-film loudspeaker with the orthogonal AgNW array.
    • Fig. S14. Theoretical values of SPL as a function of sound frequency for loudspeaker with different thickness and substrates.
    • Fig. S15. Comparison of adhesion force of various micropatterned PDMS films.
    • Fig. S16. Schematics showing the structure of microphone devices.
    • Fig. S17. Waveform and STFT signals of original sound (“There’s plenty of room at the bottom”) extracted by the sound wave analyzer, where the signal was read from a commercial microphone.
    • Fig. S18. FFTs extracted from the sound wave of the word “nanomembrane” obtained from voices of different subjects including the registrant, the authorized user, and the denied user.
    • Fig. S19. FFTs extracted from the sound wave, obtained from the voice of a registrant.
    • Fig. S20. FFTs for a test repeated 10 times, extracted from the sound wave of the word “hello” obtained from various voices of different subjects including the registrant, a man, and two women.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Mechanical durability of hybrid NM.
    • Movie S2 (.mp4 format). Compression and stretching test of hybrid NM.
    • Movie S3 (.mp4 format). Skin-attachable NM loudspeaker.
    • Movie S4 (.mp4 format). The voice recognition using NM microphone.
    • Movie S5 (.mp4 format). Voice-based security system.

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article